Extending a circuit issues

[Amp David]

Evening all,

Been asked to wire a new extension. As there are plenty of spare ways in the CU, I suggested running a new 20 Amp radial. Customer, who is a friend, says theres already a socket there (used to be a conservatory there before the extension), so why don't you use add to thiat.

My thinking was that adding to this circuit will push the Zs reading over the allowed limit for a 32 amp MCB.

Instead then, as he isn't too keen on me pulling up all the landing carpets etc, to run a new radial, I suggested FCU then running the 5 sockets he wants as a radial from this. My mate agrees, as he hasn't a clue really what i'm saying, but the other guys there today, you guessed it, the builder boys are all saying i'm mad and it'll be a botched job.

Am i mad or have i suggested the only real alternative. Just need some words of advice as only just starting to go out on my own and don't want to start off on the wrong foot.

Cheers

 

[chris gray]

spart pointing issues with their work, theyll soon shurrup

 

[Notsosmart]

Perfectly feasable to run them from a FCU but 5 sockets is stretching it.

I would go back to your original solution and run in the radial (or a new ring) or a radial in 4mm so allowing you to use a 32A (as long as all de-rating factors taken into consideration allow this)

If you feel that you may loose face, just point out that it was your original course of action.

 

[Mark_Burgess]

Take a Zs reading and see if there will be room for more, if there is not, get the BRB out and show/explain to your friend why it cant be done.

 

[Sintra]

Is the existing circuit on a ring? I am assuming that it is as you have mentioned 32A MCB.

An option would be to extend the ring circuit incorporating your new sockets.

As for the maximum Zs, the ring should already be protected by a 30mA RCD and if it is not you will have to install 1 anyway. Therefore bringing your max permitted Zs to 1667 ohms.

 

[Hawk81]

Is the existing circuit on a ring? I am assuming that it is as you have mentioned 32A MCB.

An option would be to extend the ring circuit incorporating your new sockets.

As for the maximum Zs, the ring should already be protected by a 30mA RCD and if it is not you will have to install 1 anyway. Therefore bringing your max permitted Zs to 1667 ohms.

agree totally

 

[acat]

Just ask these builders to measure the Zs and Ze ask them for the current carrying capacity of a lump of cement and does the close grouping of bricks cause inductive feedback into their trowel and is that why their brains are fried.

Chris

 

[Notsosmart]

Just ask these builders to measure the Zs and Ze ask them for the current carrying capacity of a lump of cement and does the close grouping of bricks cause inductive feedback into their trowel and is that why their brains are fried.

Chris

Meow, ouch! put your claws away Chris

I take it builders are'nt the flavour of the week.

 

[chris gray]

would it be possible to split the ring in 2 and extend one of them?

 

[acat]

You guessed it had my fill of a know it all yesterday and went to town big style hence the news today was more about the atomic bomb going off in Ceredigion than politics. Final score sparkys 10 Builders 0


Chris

 

[Des 56]

The worse case is that you have Pme and have 60898 b mcb at 1.15 (80%)
So the cable has about 0.8 left for your R1+ R2 if its not derated by the routing, thats a fair length run

I take it the existing cable is 2.5
If you intended running extra sockets for the radial the current limit will be the mcb and fitting a fused spur would not be needed, In fact it derates the circuit needlessly
The circuit would not be suitable for 32 amp if it is 2.5
20 amp would be probable

Why not say it can be done,then qualify this with the advise that, they may very well experience overload problems, depending on the load use